a = [
    291 341 411 381;
    312 402 392 412;
    322 392 372 402;
    292 402 432 352;
    362 412 272 342;
    ];

a1 = sum(a(:,1),1)/5;
a2 = sum(a(:,2),1)/5;
a3 = sum(a(:,3),1)/5;
a4 = sum(a(:,4),1)/5;